The route to fractals in magnetotelluric exploration of the crust

Abstract

Summary: Although electromagnetic induction is governed by a linear diffusion equation, the magnetotelluric method has provided evidence of fractal structures in the crust. During the search for an electrical conduction mechanism that is compatible with the geophysical anomalies in the middle and lower crust, random resistor networks were developed. They contain two types of resistors, representing the rock matrix and the conductive phase. Random resistor network models can explain both the electrical anisotropy and the lateral variability of the bulk conductivity found in large scale electromagnetic array experiments. These observations are a consequence of the very non-linear relationship between the amount of conductive material and the bulk conductivity of strongly heterogeneous media. Coincidence between the statistical properties of field data and modelled data is obtained if resistor networks with fractal geometry are employed. This can indicate that the natural conductive networks also have fractal geometry and stay close to a percolation threshold. © 2005 Springer-Verlag Berlin Heidelberg.